In line with an increase in the price of energy sources due to the depletion of fossil fuels and amplification of interests in environmental pollution, environmentally-friendly alternative energy sources have become an indispensable factor for the future life.
In particular, the demand for secondary batteries as an environmentally-friendly alternative energy source has rapidly increased as the technology development and demand for mobile devices have increased.
Typically, lithium metal has been used as a negative electrode of a lithium secondary battery, but, since it has been known that a battery short circuit may occur due to the formation of dendrites and there is a risk of explosion due to the short circuit, the lithium metal is being replaced by a carbon-base compound capable of reversibly intercalating and deintercalating lithium ions as well as maintaining structural and electrical properties.
Since the carbon-based compound has a very low discharge voltage of about −3 V with respect to a hydrogen standard electrode potential and exhibits highly reversible charge and discharge behavior due to the uniaxial orientation of a graphene layer, the carbon-based compound exhibits excellent cycle life characteristics. Also, since the carbon-based compound may exhibit a potential that is almost similar to pure lithium metal, i.e., the electrode potential of the carbon-based compound is 0 V Li/Li+ during lithium (Li)-ion charge, higher energy may be obtained when a battery is configured with an oxide-based positive electrode.
The carbon-based active material is classified into crystalline carbon and amorphous carbon, and the crystalline carbon may be classified into natural graphite and artificial graphite.
The natural graphite has excellent voltage flatness and high capacity close to theoretical capacity, but particles thereof have a highly crystalline plate shape. Thus, since the impregnation of an electrolyte solution is not facilitated due to the fact that the active material is compressed to high density when the particles are prepared as an electrode plate, high-rate charge and discharge characteristics may be reduced.
Since the artificial graphite has an excellent improvement effect on cycle life characteristics of the battery but has lower capacity than the natural graphite, a greater amount of the artificial graphite must be loaded to prepare a high-density electrode. In this case, since the artificial graphite has a low rolling property and has a high spring back effect, it is difficult to prepare a high-density electrode with targeted porosity. Thus, there is an urgent need to develop a method of preparing a high-density negative electrode for a secondary battery having improved rolling property and capacity characteristics by using a carbon-based active material.